Assessment of omega-3 PUFA reserves in the quagga mussel of Lake Ontario, with a special focus on its diet

Long-chain polyunsaturated fatty acids of omega-3 family (n-3 LC-PUFAs), namely eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), are physiologically essential compounds required for the normal growth and development of animals, including humans. These LC-PUFAs are mainly synthesized by some microalgae and transported through food webs. In contrast to many invertebrates, some bivalve molluscs can accumulate both EPA and DHA LC-PUFAs. Exotic bivalve quagga mussels invaded Lake Ontario in 1990 and reached lake-wide biomass of 910 (standard error 93) g m⁻² by 2023. We studied fatty acid (FA) level (% of total FAs) and content (mg g⁻¹ wet weight) in the quagga mussel across 3 depth zones of Lake Ontario: shallow (≤30 m), mid-depth (>30−90 m), and deep (>90 m). FA markers of diatoms, dinoflagellates, cryptophytes, green algae, cyanobacteria, and bacteria were found in the mussels in all depth zones but in different proportions, suggesting that mussel diets differed across depths. The level of EPA+DHA in quagga mussels was relatively high, comprising ∼15% of total FAs. The EPA contents of quagga mussels varied across depth zones: shallow > mid-depth > deep while the DHA contents were invariant and comprised on average 0.6−0.7 mg g⁻¹ of wet weight. In total, 4500−5000 × 10³ kg of n-3 PUFA are stored in quagga mussel biomass in Lake Ontario. However, this supply of n-3 PUFA is not fully utilized in the ecosystem because a relatively small portion of quagga mussel biomass is consumed by predators in Lake Ontario.